1. Field of the Invention
The present invention relates to the increase in the anti-knocking quality of Stratified Charge Engines by the use of a main combustion chamber with dimensions smaller than the diameter of the cylinder, direct fuel injection, installation of a squish area and prevention of combustion in the end-gas zone. In particular, the present invention relates to the reduction of the weight and the thermal load of the piston, the reduction of the thermal load of the protruding electrodes of a spark plug, and the reduction of the thermal load of the impingement surface of Stratified Charge Engines.
2. Description of the Related Art
Anti-knocking is generally held to be high in Texaco type combustion chambers, illustrated in FIG. 17, and in Watanabe type combustion chambers, illustrated in FIG. 18. These combustion chambers are basically swirl chambers. A swirl inside the combustion chamber (swirl chamber) disperses the directly injected fuel and mixture formation takes place inside the combustion chamber (swirl chamber).
However, according to the trade journal `Nainen kikan` (Internal Combustion Engines, Tokyo, Sankai-do Publishing), December 1993, p.10, the kinetic energy of the fuel jet in these combustion (swirl chamber) chambers at full load condition becomes too high, and part of the fuel jet is swept away from the combustion chamber (swirl chamber) into the cylinder. The fuel jet washed into the cylinder burns imperfectly and maximum torque is decreased. In Nainen kikan (Internal Combustion Engines, Tokyo, Sankai-d Publishing), July 1988, page 35 to 38, a Stratified Charge Engine by Impingement of Fuel Jet is discussed (hereafter "Stratified Charge Engine by Impingement of Fuel Jet", both two-cycle and four-cycle types, will be abbreviated as OSKA).
As concerns OSKA, Japanese Patent Disclosures Showa 63-1710, Showa 63-120815 and Showa 63-162928 as well as SAE-871689 have to be mentioned.
Construction and working at ignition of OSKA are depicted and explained in FIG. 19.
In OSKA, during the compression stroke an injector 5 injects fuel towards an impingement surface 3, installed inside the main combustion chamber 1'. As a result, by the working of the squish flow, a mixture layer--marked by dot--is created only inside the main combustion chamber 1' at ignition.
In OSKA, the mixture washed into the squish area 2 at combustion stroke, is rarefied and combustion in the end-gas zone, where knocking is developed easily, becomes impossible.
Accordingly, anti-knocking is higher in OSKA than in Pre-Mixture Combustion Engines, where fuel is delivered into the inside of the inlet valve.
However, concerning OSKA the following five problems do exist:
(1) As the main combustion chamber in OSKA is made as a deep cavity into the top of the piston, the top surface of the piston in contact with the hot combustion gas, is increased and the thermal load of the piston is higher, than in Pre-Mixture Combustion Engines. PA1 (2) The piston in OSKA is similar to the piston of Direct Fuel Injection Diesel Engines and accordingly longer and heavier than the piston of Pre-Mixture Combustion Engines. PA1 (3) Additionally, at the end of the combustion stroke a squish flow consisting of air--is developed along the squish area 2. Therefore, between the inner wall of the combustion chamber at the cylinder head, and the mixture layer inside the main combustion chamber 1', a lean mixture layer 8, that cannot be combusted, is formed. PA1 (4) To achieve high outputs in internal combustion engines using overhead valves, a light piston and a high fuel intake efficiency at high rotational speed--this is to say, a high square measure for the installation of inlet valves--is necessary. PA1 (5) Additionally, as the impinging part is projecting into the main combustion chamber 1', the construction of the combustion chamber in OSKA is complicated. PA1 (1) Reduction of the thermal load of the piston and the impingement part as compared with OSKA. PA1 (2) Lighter construction of the piston than in OSKA. PA1 (3) Reduction of thermal load of the electrode of the spark plug as compared with OSKA. PA1 (4) Higher possible output levels than in OSKA. PA1 (5) Simpler construction of the combustion chamber than in OSKA.
Also, in OSKA the whole of the edge 4 of the impinging surface 3 is protruding, and accordingly the thermal load of the impinging part is increased.
If the spark plug could be installed into the side wall of the main combustion chamber 1' at the top of the piston, then a normal spark plug electrode could be installed at the mixture layer. However, in this case, exchange of the spark plug is fairly difficult. Therefore, in OSKA the spark plug 6 is installed at the cylinder head near the injector 5. The electrode of the spark plug 6 is protruding into the mixture layers inside the main combustion chamber 1'. Accordingly, the thermal load of the spark plug electrode is increased.
As shown in FIG. 20, which is a plan of the cylinder heads bottom, the spark plug 6 is installed in a way that the space left for the two valves 15 in FIG. 20 is considerably narrowed. The diameter d of the valves 15 in OSKA, as displayed in FIG. 20, is smaller than the diameter D of the valves 15 in Pre-mixture Combustion Engines, shown in FIG. 21. In OSKA engines using overhead valves, the highest possible square measure of the valves, and accordingly maximum output is smaller than in Pre-mixture Combustion Engines.